I. Field
The present disclosure relates generally to communication, and more specifically to techniques for controlling the gain of a receiver in a communication system.
II. Background
A multi-carrier communication system employs multiple carriers for data transmission. These multiple carriers may be provided by orthogonal frequency division multiplexing (OFDM), discrete multi-tone (DMT), or some other multi-carrier modulation techniques. OFDM partitions the overall system bandwidth into multiple (K) orthogonal frequency subbands. These subbands are also called tones, subcarriers, bins, and so on. Each subband is associated with a respective carrier that may be modulated with data. The carriers for the K subbands may be independently modulated with data, and the K modulated carriers are added together to generate an OFDM signal.
OFDM has certain desirable characteristics, including the ability to combat multipath effects which are prevalent in a terrestrial communication system. However, a major drawback with OFDM is a high peak-to-average power ratio (PAPR) for the OFDM signal, i.e., the ratio of the peak power to the average power for the OFDM signal can be high. The high PAPR results from possible in-phase (or coherent) addition of all the carriers when they are independently modulated with data. In fact, it can be shown that the peak power can be up to K times greater than the average power for OFDM.
The high PAPR for the OFDM signal normally requires a receiver to have a larger dynamic range than for other modulated signals such as CDMA in order to handle the wide fluctuation in the power of a received OFDM signal. The larger dynamic range can complicate the design of the receiver. The high PAPR also makes it challenging to accurately estimate the power of the received OFDM signal. A reasonably accurate received power estimate may be needed to operate the receiver at a proper gain state in order to achieve good performance.
There is therefore a need in the art for techniques to control the gain of a receiver in a multi-carrier communication system.